This invention relates to a process for producing hydrochlorofluorocarbons (i.e., compounds that contain only hydrogen, fluorine, chlorine and carbon atoms, HCFCs) that are useful for producing fluorine-containing olefins, which are themselves useful as intermediates for making industrial chemicals, including polymers. HCFCs can also be used in place of chlorofluorocarbons, (i.e., compounds that contain only carbon, chlorine and fluorine atoms, CFCs) since the latter have been implicated in the depletion of stratospheric ozone and HCFCs are believed to contribute less to such depletion. More particularly, the present invention relates to a process for producing 1-chloro-1,1,3,3,3-pentafluoropropane or CF3CH2CF2Cl (also designated xe2x80x9cHCFC-235faxe2x80x9d), by photochlorinating 1,1,1,3,3-pentafluoropropane, or CF3CH2CHF2, (also designated xe2x80x9cHFC-245faxe2x80x9d).
U.S. Pat. No. 6,187,976 B1 describes the preparation of 1-chloro-1,1,3,3,3-pentafluoropropane by reacting, in the liquid or vapor phase, CCl3CH2CCl3 with hydrogen fluoride in the presence of a fluorination catalyst.
The production of CF3CH2CF2Cl occurs as an intermediate during the production of CF3CH2CHF2, as described in U.S. Pat. No. 5,728,904, incorporated herein by reference to the extent permitted. That method involves conversion of CCl3CH2CCl3 to CF3CH2CF2Cl by reaction with HF in the presence of a fluorination catalyst, selected from TiCl4, SnCl4 or mixtures thereof.
The UV catalyzed reaction of CF3CH2CHF2 and chlorine to produce CF3CH2CF2Cl is described by J. Chen et al., J. Phys. Chem. A, 1997, 101, 2648-2653, 2649. The reaction was carried out in the absence of oxygen and using a mixture of CF3CH2CF2H at a concentration range of 0.4-0.7 Torr and Cl2 at a concentration range of 3-4 Torr; the overall system diluted in 700 Torr of helium. The corresponding molar ratio of chlorine to CF3CH2CHF2 for this system ranged from 4.3 to 10:1. In this highly dilute, inert environment (at most, the reactants represented only 0.7% of the overall composition), it is said that the primary reaction products were CF3CH2CF2Cl and HCl. The conditions and process described, while suitable for academic research, are not amenable to scale-up and industrial use.
While the photochlorination of fluorine-containing hydrocarbons is described in the patent literature, it is in connection with the purification of 1,1,1,3,3-pentafluoropropane, HFC-245fa, by chlorinating olefinic impurities, U.S. Pat. Nos. 6,077,982 and 5,951,830; and the production of HCFCs (and HFCs), wherein the HCFC compounds contained more than one chlorine atom, U.S. Pat. Nos. 5,421,971 and 4,060,469. In particular, U.S. Pat. No. 6,077,982 discloses that the amount of chlorine added relative to the unsaturated impurity present can range from about 1 to 1.5 times the concentration of the unsaturated impurity (col. 3, lines 4-6) and the concentration of the unsaturated species is from about 300-20,000 wt. ppm (col. 2, lines 55-56). Based on these values, the maximum ratio of chlorine to HFC-245fa disclosed in this patent is about 0.1. While the patent discloses that increasing the amount of chlorine relative to the amount of impurity improves its chlorination and ultimate removal, the increase is within the scope of the range disclosed and there is no recognition that further increases run the risk of chlorinating or over-chlorinating the primary product, HFC-245fa. In fact, chlorination of HFC-245fa is contrary to the objectives of this patent.
There is a continuing need for the production of HFC-235fa, a useful industrial chemical, using a controlled process that produces little or no undesirable by-products.
A process for preparing 1-chloro-1,1,3,3,3-pentafluoropropane, CF3CH2CF2Cl, comprising contacting in a reaction zone in the substantial absence of oxygen reactants comprising chlorine and 1,1,1,3,3-pentafluoropropane, CF3CH2CHF2, and subjecting the reactants to actinic radiation, wherein: (A) inert gas is present at a concentration equal to or less than 5 wt. % of the total weight of said reactants; and (B) the concentration of chlorinated product produced having greater than one chlorine present in the molecule is less than or equal to about 10 wt. %.
As used herein, xe2x80x9cactinic radiationxe2x80x9d means light irradiation of sufficient intensity and at appropriate wavelengths, including ultraviolet and visible light, but preferably wavelengths shorter than those of visible light, such that the radiation causes photochemical effects, especially including chemical reaction between chlorine and 1,1,1,3,3-pentafluoropropane.
Various methods for producing 1,1,1,3,3-pentafluoropropane or HFC-245fa are described in U.S. Pat. Nos. 5,710,352; 5,969,198; and 6,023,004. Another method, described in U.S. Pat. No. 5,728,904, is said to be economical, amenable to large scale application and uses readily available raw materials. The process of that patent uses three steps, as follows: 1) formation of CCl3CH2CCl3 by the reaction of CCl4 with vinylidene chloride; 2) conversion of CCl3CH2CCl3 to CF3CH2CF2Cl by reaction with HF in the presence of a fluorination catalyst, selected from TiCl4, SnCl4 or mixtures thereof; and 3) reduction of CF3CH2CF2Cl to CF3CH2CF2H. The disclosures of each of these four patents are incorporated herein to the extent permitted. Commercial quantities of CF3CH2CHF2, or HFC-245fa, also are available from Honeywell International Inc., Morristown, N.J. for use as a reactant in the present process.
The preferred reaction of the present process between HFC-245fa and chlorine in the presence of actinic radiation causes substitution of a covalently bonded hydrogen atom in the substrate molecule by chlorine, as represented by the following equation:
CF3CH2CHF2+Cl2xe2x86x92CF3CH2CF2Cl+HCl
Undesirable multichlorinated byproducts include, for example, 1,1,1,3,3-pentafluoro-2,2,3-trichloropropane, CF3CCl2CF2Cl, and CF3CHClCF2Cl.
The apparatus used for photochlorination can be any suitable reactor capable of containing the reactants at the temperature and pressure during the photochlorination reaction and also containing an appropriate actinic radiation source or sufficiently transparent to actinic radiation in the desired wavelength range. For example, the reactor can be constructed of suitably corrosion-resistant metal, metal lined with glass or plastic, or glass, in other words a material suitably resistant to the corrosive effects of chlorine, and include a well, for example a quartz well, in which a light source is located. Alternatively, the reactor can be constructed of glass and the light source can be external to the reaction zone, but irradiating the reaction zone or focused thereon. Preferably, the reactor includes means to mix or stir reactants in the liquid and/or vapor phase and at least one condenser or cold trap in order to control the reactants and reaction products. The apparatus preferably includes at least one inlet for the reactants and at least one outlet for the reaction by-products. For example, multiple inlets are provided, one for HFC-245fa and one for chlorine. A suitable reactor consists of a glass reactor, of appropriate size for producing the quantities of product desired, equipped with a condenser or cold trap, a magnetic stirrer, and fitted with a water cooled, quartz immersion well for placement of a 450 watt, quartz, medium pressure, mercury vapor lamp, e.g., providing radiation at about 200-400 nm, and having an inlet for the introduction of chlorine and an outlet for gaseous products. Such an apparatus, having a capacity of 1 liter, is available from Ace Glass Co., Vineland, N.J. In addition, the Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 17, pages 545-555 (3d ed. 1982) contains a general description of the types of light sources and reactors that may be used; this portion of the reference is incorporated herein to the extent permitted.
Desirably the reaction zone is maintained at a temperature of from about xe2x88x925xc2x0 C. to about +10xc2x0 C.; preferably is maintained from about xe2x88x923xc2x0 C. to about +5xc2x0 C.; more preferably from about xe2x88x920xc2x0 C. to about +2xc2x0 C. Typically the reaction zone is maintained at a temperature such that HFC-245fa is present in both the liquid and vapor phase during the course of the reaction.
When it is introduced as a separate feed stream, chlorine is typically introduced into the reactor as a gas. The flow rate of the chlorine gas should be carefully regulated and controlled so that the molar ratio of chlorine relative to HFC-245fa in the reaction zone typically does not exceed about 1.5:1; preferably it does not exceed about 1.3:1; more preferably it does not exceed about 1.2:1; most preferably it does not exceed about 1.1:1. As for the minimum amount of chlorine required for the reaction, the ratio of chlorine to HFC-245fa is typically about 0.2:1; preferably about 0.3:1; more preferably, about 0.5:1; most preferably about 0.75:1; for example, about 0.9:1. Each of the expressed lower and upper concentrations can be combined to construct suitable ranges for the ratio of chlorine to HFC-245fa; for example, from about 0.2 to about 1.5; from about 0.2 to about 1.1; from about 0.5 to about 1.1; etc. The most preferred ratio is from about 1.0: to about 1.2:1. If the feed rate or amount of chlorine relative to the amount of HFC-245fa is too low, the process can be economically unattractive, e.g., the amount of chlorinated product produced is unacceptably low. Conversely, if the ratio of chlorine to HFC-245fa is too high, an excessive amount of by-products containing more than one chlorine on the hydrochlorofluorocarbon (a xe2x80x9cmultichlorinatedxe2x80x9d product) is obtained. For convenience, particularly when a batch or titration-type process is practiced (see below for a description of the latter), the molar ratio of chlorine to HFC-245fa can be calculated based on the total amount of each reactant used during the course of the process; in such event, the ratios expressed above should be maintained in order to achieve the benefits of the present invention.
Typically the product of the process will contain less than about 10 wt. % multichlorinated product; preferably less than about 6 wt. %; more preferably less than about 4 wt. %. It is particularly preferred that no such multichlorinated products be produced, but a trace level of multichlorinated product may be expected, for example from greater than about zero to less than about 1 wt. %; preferably less than about 0.5 wt. %; more preferably less than about 0.1 wt. %; still more preferably less than about 0.05 wt. %; for example from greater than zero to less than about 0.025 wt. %.
Chlorine can be fed to the reactor in several ways. It can be introduced to the reactor by way of a feed line and enter the reactor preferably by way of a sintered glass sparger, for example, submerged under liquid HFC-245fa already present in the reactor; it can be added to the vapor phase of the reactor; it can be premixed with HFC-245fa, for example, if the latter is to be fed continuously, at a distance upstream from the reactor in order to partially or thoroughly saturate the HFC-245fa before the mixture enters the reactor; it can be premixed with HFC-245fa as described and also be present in excess in the premixed stream. Preferably chlorine is fed to the reactor as a gas through a sparger under HFC-245fa that is present in the reactor as a liquid phase; and wherein chlorine and/or HFC-245fa can also be present in the vapor phase at the temperature and pressure conditions of the reactor. In this manner the chlorine can be introduced for a period of time so as to partially or fully saturate the HFC-245fa liquid prior to initiating the photochlorination reaction by providing actinic radiation.
The process of the present invention can be carried out as a batch reaction, a semi-continuous reaction or as a continuous reaction. By a semi-continuous reaction is meant where effectively all of the HFC-245fa is fed to the reaction zone and thereafter chlorine gas is introduced into the reactor, preferably sparged into the HFC-245fa at a controlled rate. During the course of the reaction chlorine gas is introduced in a controlled manner to maintain the ratio of chlorine to HFC-245fa at a suitable level, until most of the HFC-245fa is consumed. Additional HFC-245fa can be added to maintain the ratio of reactants at the desired level, as described above. Such a process can also be considered to be a titration-type process, since the titrating agent, chlorine, is added to HFC-245fa in a substantially continuous manner until the desired end-point is reached, e.g., until the HFC-245fa is sufficiently consumed that the reaction is terminated. Suitable analytical monitoring means, e.g., gas chromatography, can be employed to ascertain the concentrations of HFC-245fa and/or HCFC-235fa so as to avoid an excessively high ratio of chlorine to HFC-245fa.
Preferably the reaction is carried out in a substantially oxygen-free environment. This can be accomplished by, for example, flushing the reactor with an inert gas such as nitrogen, helium, argon, etc., prior to carrying out the reaction; nitrogen is preferred. It is expected that such an inert gas is itself substantially free of oxygen. Suitable commercial nitrogen is available that contains from about 100 ppm to about 2 wt. % oxygen and at levels in between including 0.1, 0.2, 0.5 and 1 wt. % oxygen. Nitrogen containing the lowest oxygen level commensurate with good economics should be used for the process. If nitrogen is used to flush the system, the nitrogen is preferably flushed from the reactor, e.g., with chlorine and/or HFC-245fa, before the reactants are introduced and the actinic radiation is activated. Alternatively, the use of nitrogen or an inert gas can be avoided and the reactor can be flushed with chlorine and/or HFC-245fa prior to carrying out the reaction. In any event, it is preferred that the reactor be substantially free of inert gas at the start of the reaction. In this context, substantially free means that the reactor contains less than about 10 weight % inert gas; more preferably less than about 5%; still more preferably less than about 3%; for example from less than about 1% to about 2%. In the preferred method of carrying out the process of the present invention, the reaction is carried out in the substantial absence of an inert gas such as nitrogen or helium; in other words, only the reactants and products of the reaction are present in the reaction zone except for the possible presence of trace levels of an inert gas diluent, e.g., less than about 1 wt. % of such a material.
The pressure in the reaction zone is not a critical variable for the process of the present invention. For example, the pressure can vary from slightly less than ambient pressure of one atmosphere (about 101 kPa) to a pressure somewhat greater than one atmosphere; generally the process can be carried out under pressures of from about one atmosphere up to about 3.5 atmospheres (about 354 kPa). Suitable account should be taken of the fact that the reactants, the desired product CF3CH2CF2Cl, or HCFC-235fa, and by-product HCl can have significant vapor pressure. In particular, if the process is carried out in a closed system as a batch process, the changing amounts of reactants and reaction products should be taken into account to avoid excessive pressure build-up.
The source of irradiation for the photochlorination is not critical and it may be provided by any conventional source such as sun lamps, mercury vapor lamps (high, medium and low pressure types), bright incandescent and fluorescent lamps. Although any type of irradiation may be suitable, including visible light and ultraviolet light, ultraviolet light is preferred. The wavelength of the light can be from about 2000 to about 14500 Angstroms; for example from about 2500 to about 14000 Angstroms. The light source preferably radiates at from about 2700 Angstroms to about 5000 Angstroms; more preferably from about 2000 Angstroms to about 5000 Angstroms; most preferably from about 3000 Angstroms to about 4000 Angstroms. No advantage accrues from using radiation having wavelengths above about 5000 Angstroms.
As described above, the photochlorination reaction produces HCl in addition to the desired product. In one embodiment, following reaction or contact of the reactants in the presence of actinic radiation, the reactants and reaction products, including HCl, HCFC-235fa and possible multichlorinated products are contacted with an aqueous solution selected from the group consisting of a metal bisulfite, carbonate and hydroxide wherein the metal is selected from the group consisting of Group 1 and Group 2 according to the New Notation of the Periodic Table of the Elements. In particular, HCl can be removed from the product stream using conventional means such as absorption by a water or caustic scrubber, or distillation. The desired reaction product, HCFC-235fa can be separated from the overall reaction product stream or composition, which may include multichlorinated product, by using conventional means such as fractionation, distillation or liquid-liquid extraction. Unreacted HFC-245fa can be recycled back to the photochlorination reaction provided that it is treated to avoid undesirable impurities that may be present as a result of the separation processes, e.g., water. The effluent from the reactor also includes unreacted chlorine gas that can first be separated and purified by conventional methods and recycled.
All references herein to elements or metals belonging to a certain Group refer to the Periodic Table of the Elements as it appears in Hawley""s Condensed Chemical Dictionary, 13th Edition. Also, any references to the Group or Groups shall be to the Group or Groups as reflected in this Periodic Table of Elements using the xe2x80x9cNew Notationxe2x80x9d system for numbering groups.
The following examples are given as specific illustrations of the invention. It should be understood, however, that the invention is not limited to the specific details set forth in the examples. All parts and percentages in the examples, as well as in the remainder of the specification, are by weight unless otherwise specified.
Further, any range of numbers recited in the specification or paragraphs hereinafter describing or claiming various aspects of the invention, such as that representing a particular set of properties, units of measure, conditions, physical states or percentages, is intended to literally incorporate expressly herein by reference or otherwise, any number falling within such range, including any subset of numbers or ranges subsumed within any range so recited. The term xe2x80x9caboutxe2x80x9d when used as a modifier for, or in conjunction with, a variable, is intended to convey that the numbers and ranges disclosed herein are flexible and that practice of the present invention by those skilled in the art using temperatures, concentrations, amounts, contents, carbon numbers, and properties that are outside of the range or different from a single value, will achieve the desired result, namely, photochlorination process for the preparation of chlorinated HFC-245fa, or HCFC-235fa.